1. Field of the Invention
The present invention relates to a toner and a developer, specifically to a toner which has excellent fixability and heat resistance storage stability and which can be suppressed in the occurrence of filming.
2. Description of the Related Art
In recent years, toners have been required to have the following: small particle diameters for forming high-quality images; low temperature fixability for hot offset resistance and energy saving; and heat resistance storage stability durable to high-humidity, high-temperature conditions during storage and transportation after production. In particular, it is quite important to improve low temperature fixability, since the power consumption upon fixing accounts for most of the total power consumption in the image forming process.
Conventionally, there have been used toners produced by the kneading pulverizing method. These toners are difficult to have small particle diameters, and their shapes are indefinite and their particle size distribution is broad. Thus, the toners produced by the kneading pulverizing method cannot form images having satisfactory quality and problematically require high energy for fixing. Also, when toner materials including wax (releasing agent) for improving fixing ability are used to produce a toner by the kneading-pulverizing method, cracks occur at the interfaces of the wax during pulverization, resulting in that the wax exists on the toner surface in a large amount. As a result, although the releasing effects can be obtained, toner adhesion to a carrier (filming), a photoconductor and a blade is likely to occur. The properties of such toners are not satisfactory in total.
In order to overcome the above-described problems the kneading-pulverizing method has, there is proposed a method for producing a toner by the polymerization method. According to the polymerization method, toners are made easily to have a small particle diameter. Their particle size distribution is sharper than that of the toners obtained by the pulverizing method. Furthermore, the releasing agent can be embedded in the toner particles. As one exemplary polymerization method, Japanese Patent Application Laid-Open (JP-A) No. 11-133665 and other patent literatures disclose a method for producing a toner using, as a binder, an elongated product of a urethane-modified polyester for the purposes of improving low-temperature fixing ability and hot offset resistance of toner.
Also, JP-A Nos. 2002-287400 and 2002-351143 and other patent literatures disclose a production method for a toner having excellent fluidity and transferability as powder with a small particle diameter as well as being excellent in heat resistant storage stability, low-temperature fixing ability and hot offset resistance.
Japanese Patent (JP-B) No. 2579150 and JP-A No. 2001-158819 disclose a toner production method including an aging step for producing a toner binder having a more uniform molecular weight distribution and for attaining both desired low-temperature fixing ability and desired offset resistance.
None of these proposed techniques meet such a high level of low temperature fixability that has recently been required.
In order to produce a toner having a high level of low temperature fixability, there has been proposed a toner including: a resin containing a crystalline polyester resin; and a releasing agent, wherein the resin and the wax are not in a compatible state to form a phase-separated, sea-island structure (for example, JP-A No. 2004-46095).
Also, there has been proposed a toner containing a crystalline polyester resin, a releasing agent and a graft polymer (for example, JP-A No. 2007-271789).
These proposed techniques can produce toners having good heat resistance storage stability, good hot offset resistance, and a high level of low temperature fixability. However, the crystalline polyester resin and the releasing agent are not sufficiently dispersed in the toners, causing filming.
Furthermore, the toners containing the crystalline polyester are excellent in low temperature fixability but poor in blocking property of the toner image after fixing. When printed matter having toner image is stored at high temperatures, the image tends to melt to be peeled off, which is problematic.
Thus, at present, demand has arisen for a toner which involves no filming and which has excellent low temperature fixability, hot offset resistance, heat resistance storage stability, and blocking resistance of the toner image after fixing; and a developer containing the toner.